Method for removing cyclic hydrocarbons from an aqueous solution using an active adsorptive nanocomposite

ABSTRACT

The removal of cyclic hydrocarbons from water sources and systems using an active adsorptive nanocomposite comprising multi-walled carbon nanotubes impregnated with metal oxide nanoparticles on the surface of and/or within the carbon nanotubes. A process for producing the active adsorptive nanocomposite is also provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation of Ser. No. 14/963,777, havinga filing date of Dec. 9, 2015, now allowed.

BACKGROUND OF THE INVENTION Technical Field

The present disclosure relates to a method for the removal of cyclichydrocarbons from water sources and systems using an active adsorptivenanocomposite, and a process for synthesizing the active adsorptivenanocomposite.

Description of the Related Art

The “background” description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description which may nototherwise qualify as prior art at the time of filing, are neitherexpressly or impliedly admitted as prior art against the presentinvention.

Toluene and para-xylene are established cyclic hydrocarbons contaminantsin water sources. These compounds are classified as flammable, toxic,carcinogenic and/or mutagenic [W. J. Deutsch and R. Siegel, GroundwaterGeochemistry: Fundamentals and Applications to Contamination. CRC Press,1997, p. 232.; and C. Kent, Basics of Toxicology, vol. 13. John Wiley &Sons, 1998, p. 194.—each incorporated herein by reference in itsentirety]. Thus, their presence in aqueous solution is a significantenvironmental concern, even at low concentrations. The health effectsthese pollutants cause in humans include disturbance of the kidney,liver and blood systems, skin and sensory irritation, respiratoryproblems, cancer, leukemia, and central nervous system depression. As aresult of these health concerns, the U.S. EPA has set a maximumcontaminant level of 10 mg/L for xylene in drinking water and the U.S.Public Health Service has recommended no more than 1 mg/L of toluene inwater for lifetime exposure.

These compounds are widely used in several chemical production andmanufacturing processes including petroleum refiners, as well as thepolymer, plastic and paint industries as solvent, a natural fraction ofpetroleum and as precursors for the manufacturing of differentchemicals. Water draining from these industries is highly contaminatedwith toluene and para-xylene and the pollutants must be removed beforewater is discharged from any of these industrial facilities [J. A. Kent,Kent and Riegel's Handbook of Industrial Chemistry and Biotechnology:Vol. 1. Springer Science & Business Media, 2010, p. 391.; and John J.McKetta Jr, Encyclopedia of Chemical Processing and Design: Volume67—Water and Wastewater Treatment: Protective Coating Systems toZeolite. CRC Press, 1999, p. 289.—each incorporated herein by referencein its entirety]. Further, the pollutants are frequently found ingroundwater due to inadvertent spills during production and/ortransportation, leaks in underground storage tanks and pipelines,leaching from landfills and improper waste disposal practices. Thesepollutants migrate easily in the water system, with little or notendency of being confined near the origin of contamination.

There have been many studies aimed at the removal of cyclic hydrocarbonssuch as benzene from water. The reported remediation methods include wetair oxidation [B. A. Abussaud, N. Ulkem, D. Berk, and G. J. Kubes, “WetAir Oxidation of Benzene,” Ind. Eng. Chem. Res., vol. 47, no. 514, pp.4325-4331, 2008.—incorporated herein by reference in its entirety],photo catalytic degradation [M. Bahmani, V. Bitarafhaghighi, K. Badr, P.Keshavarz, and D. Mowla, “The photocatalytic degradation and kineticanalysis of BTEX components in polluted wastewater by UV/H₂O₂-basedadvanced oxidation,” Desalin. Water Treat., vol. 52, no. 16-18, pp.3054-3062, May 2013.; and M. N. Chong, B. Jin, C. W. K. Chow, and C.Saint, “Recent developments in photocatalytic water treatmenttechnology: a review.,” Water Res., vol. 44, no. 10, pp. 2997-3027, May2010.—each incorporated herein by reference in its entirety], andadsorption using various materials [I. Ali and V. K. Gupta, “Advances inwater treatment by adsorption technology.,” Nat. Protoc., vol. 1, no. 6,pp. 2661-7, January 2006.—incorporated herein by reference in itsentirety]. However, each technique is characterized by its inherentlimitations, which create the continuous need for improvements inmethods for the specific removal of toluene and para-xylene fromcontaminated water sources.

Adsorption has become one of the most promising and increasinglypracticed industrial techniques for removing cyclic hydrocarbons such aspara-xylene, and toluene from water using such varied absorbents assand, peat and activated carbon [Y. Kalmykova, N. Moona, A.-M.Stromvall, and K. Björklund, “Sorption and degradation of petroleumhydrocarbons, polycyclic aromatic hydrocarbons, alkylphenols, bisphenolA and phthalates in landfill leachate using sand, activated carbon andpeat filters.,” Water Res., vol. 56, no. 0, pp. 246-57, June 2014.; andN. Wibowo, L. Setyadhi, D. Wibowo, J. Setiawan, and S. Ismadji,“Adsorption of benzene and toluene from aqueous solutions onto activatedcarbon and its acid and heat treated forms: influence of surfacechemistry on adsorption.,” J. Hazard. Mater., vol. 146, no. 1-2, pp.237-42, July 2007; and C. L. Mangun, Z. Yue, J. Economy, S. Maloney, P.Kemme, and D. Cropek, “Adsorption of Organic Contaminants from WaterUsing Tailored ACFs,” no. June 1996, pp. 2356-2360, 2001.—eachincorporated herein by reference in its entirety].

Carbon nanotubes (CNTs) have attracted great interest as adsorbentsbecause of their unique chemical structure and intriguing electrical,mechanical and physical properties facilitating the adsorption ofdifferent chemicals including organic, inorganic and biologicalmaterials [W. Chen, L. Duan, and D. Zhu, “Adsorption of Polar andNonpolar Organic Chemicals to Carbon Nanotubes,” Environ. Sci. Technol.,vol. 41, no. 24, pp. 8295-8300, December 2007.; and V. K. Gupta, S.Agarwal, and T. a Saleh, “Chromium removal by combining the magneticproperties of iron oxide with adsorption properties of carbonnanotubes.,” Water Res., vol. 45, no. 6, pp. 2207-12, March 2011.—eachincorporated herein by reference in its entirety]. These carbonnanotubes have high surface areas, are easily modified on their surfaceto aid adsorption, and are especially well-suited to waste watertreatment [O. G. Apul and T. Karanfil, “Adsorption of Synthetic OrganicContaminants by Carbon Nanotubes: A Critical Review,” Water Res., vol.68, pp. 34-55, October 2014.; and X. Qu, P. J. J. Alvarez, and Q. Li,“Applications of nanotechnology in water and wastewater treatment.,”Water Res., vol. 47, no. 12, pp. 3931-3946, August 2013.; and X. Liu, M.Wang, S. Zhang, and B. Pan, “Application potential of carbon nanotubesin water treatment: A review,” J. Environ. Sci., vol. 25, no. 7, pp.1263-1280, July 2013.—each incorporated herein by reference in itsentirety].

Despite many studies indicating that CNTs have a high affinity foradsorbing organic chemicals and the potential for developing carbonnanotubes for cyclic hydrocarbon water treatment and removal [C.-J. M.Chin, M.-W. Shih, and H.-J. Tsai, “Adsorption of nonpolar benzenederivatives on single-walled carbon nanotubes,”Appl. Surf. Sci., vol.256, no. 20, pp. 6035-6039, August 2010.; and F. Tournus and J.-C.Charlier, “Ab initio study of benzene adsorption on carbonnanotubes,”Phys. Rev. B, vol. 71, no. 16, p. 165421, April 2005.; and Y.Liu, J. Zhang, X. Chen, J. Zheng, G. Wang, and G. Liang, “Insights intothe adsorption of simple benzene derivatives on carbon nanotubes,” RSCAdv., vol. 4, no. 101, pp. 58036-58046, October 2014—each incorporatedherein by reference in its entirety] there remains many possibilitiesfor developing different types of carbon nanotubes with differentmorphologies [S. Iijima, “Helical microtubules of graphitic carbon,”Nature, vol. 354, no. 6348, pp. 56-58, 1991.—incorporated herein byreference in its entirety] and functionalization for enhancing theiraffinity for specific contaminants and improving their removalefficiencies as adsorbents.

Surface modification of carbon nanotubes to enhance cyclic hydrocarbonsadsorption from aqueous solutions has proven effective. For example, Suet al. employed multi-walled carbon nanotubes (MWCNTs) that wereoxidized by sodium hypochlorite (NaOCl) solution to enhance theadsorption of benzene and toluene from aqueous solution [F. Su, C. Lu,and S. Hu, “Adsorption of benzene, toluene, ethylbenzene and p-xylene byNaOCl-oxidized carbon nanotubes,” Colloids Surfaces A Physicochem. Eng.Asp., vol. 353, no. 1, pp. 83-91, January 2010.—incorporated herein byreference in its entirety]. NaOCl-oxidized CNTs have superior adsorptionperformance compared with many types of carbon and silica adsorbentspreviously reported in the literature. The work has been extended toadditional cyclic hydrocarbons including xylene and ethyl benzene [F.Yu, J. Ma, and Y. Wu, “Adsorption of toluene, ethylbenzene and xyleneisomers on multi-walled carbon nanotubes oxidized by differentconcentration of NaOCl,” Front. Environ. Sci. Eng. China, vol. 6, no. 3,pp. 320-329, June 2011.—incorporated herein by reference in itsentirety].

In view of the foregoing, one object of the present disclosure is toprovide a metal oxide nanoparticle impregnated carbon nanotubenanocomposite for targeted adsorptive removal of cyclic hydrocarbonpollutants and processes for economically producing those compositesthat can efficiently and at a low cost treat cyclic hydrocarboncontaminated water.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect, the present invention relates to a methodfor removing an cyclic hydrocarbon from an aqueous solution comprisingpara-xylene, toluene, or both, the method involving i) contacting anactive adsorptive nanocomposite with the first aqueous solution toadsorb at least a portion of para-xylene, toluene, or both onto at leastone surface of the active adsorptive nanocomposite, and ii) removing theactive adsorptive nanocomposite with adsorbed para-xylene, toluene, orboth to form a treated aqueous solution that has a lower para-xyleneand/or toluene content than the first aqueous solution, wherein theactive adsorptive nanocomposite comprises carbon nanotubes, and one ormore metal oxide nanoparticles selected from the group consisting ofaluminum oxide, zinc oxide, and iron oxide attached to a surface of thecarbon nanotubes, wherein the metal oxide nanoparticles are present in1-15% by weight, relative to the total weight of the active adsorptivenanocomposite.

In one embodiment, the contacting comprises mechanically mixing and/orsonicating the active adsorptive nanocomposite with the first aqueoussolution.

In one embodiment, the active adsorptive nanocomposite is mechanicallymixed with the first aqueous solution with a mechanical mixing speed ofat least 200 rpm.

In one embodiment, the active adsorptive nanocomposite is contacted withthe first aqueous solution at a weight per volume ratio of at least25-150 mg of the active adsorptive nanocomposite per 100 mL of the firstaqueous solution.

In one embodiment, the contacting is carried out for 20 min to 720 min.

In one embodiment, the active adsorptive nanocomposite is contacted withthe first aqueous solution at a temperature range of 20° C. to 30° C.

In one embodiment, the first aqueous solution is a waste water stream.

In one embodiment, the waste water stream comprises at least 100 ppm ofpara-xylene and/or toluene.

In one embodiment, the carbon nanotubes are multi-walled carbonnanotubes.

In one embodiment, the metal oxide nanoparticles are zinc oxide and thecontacting removes at least 77% of para-xylene from the first aqueoussolution.

In one embodiment, the metal oxide nanoparticles are iron oxide and thecontacting removes at least 68% of para-xylene from the first aqueoussolution.

In one embodiment, the metal oxide nanoparticles are aluminum oxide andthe contacting removes at least 75% of para-xylene from the firstaqueous solution.

In one embodiment, the metal oxide nanoparticles are zinc oxide thecontacting removes at least 11% of toluene from the first aqueoussolution.

In one embodiment, the metal oxide nanoparticles are iron oxide and thecontacting removes at least 17% of toluene from the first aqueoussolution.

In one embodiment, the metal oxide nanoparticles are aluminum oxide andthe contacting removes at least 17% of toluene from the first aqueoussolution.

In one embodiment, the waste water stream has a pH range from 5-7.

According to a second aspect, the present invention relates to a processfor forming an active adsorptive nanocomposite comprising i) sonicatinga sufficient amount of multi-walled carbon nanotubes in a polar solventto form a dispersion comprising deagglomerated carbon nanotubes, ii)mixing a solution comprising a metal salt dissolved in the polar solventwith the dispersion to form a nanocomposite solution wherein the metalsalt is at least one selected from the group consisting of aluminumnitrate, zinc nitrate, and iron nitrate, iii) removing the polar solventfrom the nanocomposite solution to form a dry nanocomposite; and iv)calcining the dry nanocomposite to form the active adsorptivenanocomposite wherein the active adsorptive nanocomposite comprisesmulti-walled carbon nanotubes, and one or more metal oxide nanoparticlesselected from the group consisting of aluminum oxide, zinc oxide, andiron oxide attached to the surface of the carbon nanotubes.

In one embodiment, the polar solvent is an alcohol.

In one embodiment, the polar solvent is removed from the nanocompositesolution at a temperature of at least 90° C.

In one embodiment, the dry nanocomposite is calcined at a temperature ofat least 350° C.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a scanning electron microscope (SEM) micrograph of rawmulti-walled carbon nanotubes (MWCNTs).

FIG. 1B is a SEM micrograph of zinc oxide nanoparticle impregnatedMWCNTs.

FIG. 1C is a SEM micrograph of iron oxide nanoparticle impregnatedMWCNTs.

FIG. 1D is a SEM micrograph of aluminum oxide nanoparticle impregnatedMWCNTs.

FIG. 2 is a thermal gravimetric analysis (TGA) of raw and modifiedMWCNTs.

FIG. 3A is an X-ray diffraction (XRD) spectra of raw MWCNTS.

FIG. 3B is an X-ray diffraction (XRD) spectra of zinc oxide nanoparticleimpregnated MWCNTs.

FIG. 3C is an X-ray diffraction (XRD) spectra of iron oxide nanoparticleimpregnated MWCNTs.

FIG. 3D is an X-ray diffraction (XRD) spectra of aluminum oxidenanoparticle impregnated MWCNTs.

FIG. 4 illustrates the effect of contact time on removal efficiency ofpara-xylene for raw and metal oxide impregnated MWCNTs.

FIG. 5A illustrates the effect of active adsorptive nanocomposite dosageon removal efficiency of para-xylene for raw and metal oxide impregnatedMWCNTs.

FIG. 5B illustrates the effect of active adsorptive nanocomposite dosageon removal efficiency of Toluene for raw and metal oxide impregnatedMWCNTs.

FIG. 6A is an energy dispersive X-ray (EDX) spectra for raw MWCNTs.

FIG. 6B is an energy dispersive X-ray (EDX) spectra for zinc oxideimpregnated MWCNTs.

FIG. 6C is an energy dispersive X-ray (EDX) spectra for aluminum oxideimpregnated MWCNTs.

FIG. 6D is an energy dispersive X-ray (EDX) spectra for iron oxideimpregnated MWCNTs.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Processes for removing cyclic hydrocarbons from water sources are knownto be ineffective at removing low concentrations of dissolved cyclichydrocarbons due to active materials with low surface areas, and limitedhydrocarbon specificity in the active adsorptive materials used.Therefore, a process for removing cyclic hydrocarbons in high yieldusing active adsorptive nanocomposites impregnated with different metaloxide nanoparticles is advantageous.

According to a first aspect, the present invention relates to a methodfor removing a cyclic hydrocarbon from a first aqueous solution whereinthe method includes contacting an active adsorptive nanocomposite with afirst aqueous solution in a ratio to adsorb at least a portion ofpara-xylene, toluene, or both onto at least one surface of the activeadsorptive nanocomposite.

In one embodiment, an exemplary active adsorptive nanocomposite to firstaqueous solution ratio may be 25-150 mg/100 mL.

A cyclic hydrocarbon as used herein could refer to any chemical speciescomprising a cyclic ring structure and/or at least one carbon to carbondouble bond. In one embodiment, the cyclic hydrocarbon is selected fromthe group consisting of, toluene, para-xylene, ethyl benzene, and/or anycombination thereof.

In a preferred embodiment, the cyclic hydrocarbon is selected from agroup consisting of toluene, para-xylene or both.

It is envisioned that the disclosed invention may be adapted to increasethe removal of other cyclic hydrocarbons from aqueous solutions.Examples of other cyclic hydrocarbons include, but are not limited to,mesitylene, durene, 2-phenylhexane, biphenyl, styrene, naphthalene,phenol, aniline, nitrobenzene, benzoic acid, acetylsalicylic acid,paracetamol, picric acid, anthracene, phenanthrene, tetracene, chrysene,triphenylene, pyrene, pentacene, corannulene, coronene, ovalene,benzo[a]pyrene, benzo[ghi]perylene, acenaphthene, acenaphthylene,benzo[a]anthracene, benzo[e]pyrene, benzo[b]fluoranthene,benzo[j]fluoranthene, benzo[k]fluoranthene, dibenz[a,h]anthracene,fluoranthene, fluorine, indeno[1,2,3-cd]pyrene, phenanthrene,dicyclopentadiene and mixtures thereof.

It is also envisioned that the disclosed invention may be adapted toincorporate and increase the removal of volatile organic compounds(VOCs) from aqueous solutions. Examples of volatile organic compounds(VOCs) include, but are not limited to, methyl tertiary butyl ether(MTBE), carbon tetrachloride, p-dichlorobenzene, trichloroethylene,vinyl chloride, 1,1,1-trichloroethane, 1,1-dichloroethylene,1,2-dichloroethane, cis-1,2-dichloroethylene, monochlorobenzene,cholorobenzene, o-dichlorobenzene, tetrachloroethylene,trans-1,2-dichloroethylene, 1,2-dichloropropane, dichloromethane,1,1,2-trichloroethane, 1,2,4-trichlorobenzene, perchloroethylene,chlorofluorocarbons, and mixtures thereof.

The active adsorptive nanocomposite as used herein refers to amulti-component material wherein at least one of the components has atleast one, two, or three dimensions of less than 100 nm. In general, themechanical, electrical, thermal, optical, electrochemical and catalyticproperties of the nanocomposite could differ from that of the componentmaterials as the respective phase dimension decrease below 100 nm.

In the present disclosure, the active adsorptive nanocomposite includescarbon nanotubes, and one or more metal oxide nanoparticles selectedfrom the group consisting of aluminum oxide, zinc oxide, and iron oxideattached to a surface of the carbon nanotubes. Carbon nanotubes (CNTs)as used herein refer to allotropes of carbon with a cylindricalnanostructure with a significantly large length-to-diameter ratio (up to100, 000,000:1). These cylindrical carbon molecules have unusualproperties, which are valuable for nanotechnology, electronics, opticsand other fields of materials science and technology. In particularowing to their extraordinary thermal conductivity and mechanical andelectrical properties, carbon nanotubes find applications as additivesto various structural materials.

A carbon nanotube composition comprises a hollow porous structure with“walls” formed by one-atom-thick sheets of carbon, called graphene.These sheets are rolled at specific and discrete (“chiral”) angles, andthe combination of the rolling angle and radius determines the nanotubeproperties, while imbuing the nanotubes with large surface areas ofreactive unsaturated carbon atoms. Furthermore, nanotubes arecategorized as single-walled nanotubes (SWNTs) or multi-walled nanotubes(MWNTs).

In one embodiment, the carbon nanotubes of the present disclosure are“raw” or lacking any surface functionalization or modifications. It isenvisioned that the present invention may be adapted to incorporatesurface functionalized and/or surface modified carbon nanotubes. Thesesurface modifications may be covalent, non-covalent or mixtures thereof.Examples of functional groups on the carbon nanotubes include alcoholic,carboxylic, aldehydic, ketonic and esteric oxygenated functional groups.Alternatively, the carbon nanotubes of the present disclosure may besurface modified with amine functionality or other functionality that isproton absorbing or basic.

In one embodiment, the raw carbon nanotubes may be treated with an acidsuch as HNO₃, HF, HCl and H₂SO₄. The acid treatment may enhance theadsorption properties and affect the pore size and/or surfacecharacteristics of the carbon nanotubes. Alternatively, the raw carbonnanotubes may be treated with a base such as NaOH. The base treatmentmay enhance the adsorption properties and affect the pore size and/orsurface characteristics of the carbon nanotubes.

Multi-walled nanotubes consist of multiple rolled layers (concentrictubes) of graphene. There are two models that can be used to describethe structures of multi-walled nanotubes. In the Russian Doll model,sheets of graphite are arranged in concentric cylinders, for example, asingle-walled nanotube within a larger single-walled nanotube. In theParchment model, a single sheet of graphite is rolled in around itself,resembling a scroll of parchment or a rolled newspaper. The interlayerdistance in multi-walled nanotubes is close to the distance betweengraphene layers in graphite. The Russian Doll structure is observed morecommonly, its individual shells can be described as SWNTs. In eithermodel, the number of active binding sites per volume of carbon MWNTs(MWCNTs) vs carbon SWNTs (SWCNTs) is larger, making it a more robuststructural material for the active adsorptive nanocomposite. In oneembodiment, the carbon nanotubes are multi-walled carbon nanotubes. Inone embodiment, the carbon nanotubes are mixture of SWNTs and MWNTs.

Carbon nanotubes exhibit strong adsorption affinities to a wide range ofcyclic and aliphatic contaminants in water. The large adsorptioncapacity of CNTs for organic material is primarily due to their porestructure and their large hydrophobic surface areas. Carbon nanotubesshow similar adsorption capacities as activated carbons in the presenceof natural organic matter. Highly-purified metal-impregnated carbonnanotubes have advantageous properties and performance in removingcyclic hydrocarbons from aqueous solutions when compared to conventionalapproaches due to their ability to direct the selective uptake of cyclichydrocarbon species based both on the nanotube's controlled pore size,high surface area and ordered chemical structure. Thus, they are anadvantageous adsorbent material for targeted contaminant removal inwater and wastewater treatment systems as well.

Nanoparticles as used herein refer to particles between 1 and 100 nm insize. When compared to their respective bulk materials, nanoparticlesdisplay distinctive chemical and physical properties due to size relatedquantum confinement effects. Luminescence, surface area, catalytictendencies, electrical conductivity, and magnetization can all bealtered by changes in the dimensionality of nanoparticles.

Metal oxide nanoparticles within the tubular cavity and/or on thesurface of the carbon nanotubes occupy voids within the porousstructure. Incorporating nanoparticles, which generally have a highsurface area and enhanced catalytic sensitivity, could provide anadditional surface for cyclic hydrocarbon adsorption when coupled tocarbon nanotubes. Further, the selectivity of the active nanocompositetowards different aromatic hydrocarbons can be changed by changing themetal of the metal oxide.

In one embodiment, the metal oxide nanoparticles of the presentdisclosure can be synthesized and formed into a variety of morphologiesand may refer to nanoparticles, nanocrystals, nanospheres,nanoplatelets, nanowires, nanorods, nanotubes, nanocylinders, nanoboxes,nanostars, tetrapods, nanobelts, nanoflowers, etc. and mixtures thereof.

In a preferred embodiment, the active adsorptive nanocomposite of thepresent disclosure includes metal oxide nanoparticles comprising atleast one selected from the group consisting of aluminum oxide, ironoxide, and zinc oxide.

In one embodiment, the nanocomposite comprises metal oxide nanoparticleswith crystal nanoparticle morphology and an average particle size of1-40 nm, preferably 1-35 nm, preferably 1-15 nm.

The percentage of metal oxide “impregnated” on the carbon nanotubes mayalso affect the adsorption characteristics of the active adsorptivenanocomposite. In a preferred embodiment, the active adsorptivenanocomposite comprises metal oxide nanoparticles in a range of 5-15%,preferably 8-12% or about 10% by weight, relative to the total weight ofthe active adsorptive nanocomposite.

Different metal oxides may result in preferential binding affinities fordifferent contaminants. Therefore, a single adsorptive nanocompositecould be made to target more than one contaminant. In one embodiment,the active nanocomposite comprises zinc oxide, aluminum oxide and ironoxide nanoparticles, wherein para-xylene and/or toluene are targeted forabsorption.

“Active” as used herein refers to any material, reaction or process thatis in a physical state, chemical phase and/or both to initiate asubsequent chain of events without any further alterations or adjustmentto it.

Nanoparticle and nanocomposite characterization is necessary toestablish understanding and control of nanoparticle and nanocompositesynthesis, assembly and applications. In one embodiment, the metal oxidenanoparticles and active adsorptive nanocomposite are characterized byat least one instrument selected from the group consisting of a scanningelectron microscope, a thermogravimetric analyzer, an X-raydiffractometer.

In another embodiment, it is envisioned that characterization is doneusing a variety of other techniques. Common exemplary techniquesinclude, but are not limited to, electron microscopy (TEM), atomic forcemicroscopy (AFM), dynamic light scattering (DLS), Fourier transforminfrared spectroscopy (FTIR), matrix-assisted laserdesorption/ionization time-of-flight mass spectrometry (MALDI-TOF),ultraviolet-visible spectroscopy, Rutherford backscattering spectrometry(RBS), dual polarization interferometry and nuclear magnetic resonance(NMR).

The first aqueous solution as used herein could refer to any watersource or system comprising a sufficient amount of a cyclic hydrocarbonspecies. Examples of such water sources and systems include, but are notlimited to, surface water that collects on the ground or in a stream,aquifer, river, lake, reservoir or ocean, ground water that is obtainedby drilling wells, run-off, industrial water, public water storagetowers, public recreational pools, an industrial waste water stream andbottled water. In one embodiment, the aqueous solution is a waste waterstream.

As used herein, a “sufficient amount” could be any quantity of aparameter, and/or component that produces a desired product and orreaction when applied. In the case of the disclosed invention, thedesired product and/or reaction is an adsorption of at least a portionof the cyclic hydrocarbon from the first aqueous solution onto at leastone surface of the active nanocomposite.

In the present disclosure “contacting” could refer to any process ofinteracting different chemical components in order to foster a chemicalor physical change between the components. In one embodiment, thecontacting comprises mechanically mixing the active adsorptivenanocomposite with the first aqueous solution. In one preferredembodiment, the contacting comprises sonicating the active nanocompositewith the first aqueous solution.

Adsorption or adsorb as used herein may refer to the adhesion of atoms,ions or molecules from a gas, liquid or dissolved solid to a surface.This process creates a film of the adsorbate on the surface of theadsorbent. This process differs from absorption, in which a fluid (theadsorbate) permeates or is dissolved by a liquid or solid (theabsorbent). Adsorption is a surface-based process while absorptioninvolves the whole volume of the material. The term sorption encompassesboth processes, while desorption is the reverse of it. Adsorption is asurface phenomenon. In one embodiment, the cyclic hydrocarbon isadsorbed onto a surface of nanocomposite during the contacting, whereinthe cyclic hydrocarbon adheres to the at least one surface of the carbonnanotube, a surface of metal oxide nanoparticle, or both.

How efficiently the adsorption occurs in the disclosed method may bedependent upon a number of parameters. The rate of the contacting, thecontacting time, the active nanocomposite dosage, the temperature duringthe contacting, the first aqueous solution pH and the metal oxidenanoparticle used in the active nanocomposite could all be adjusted tovary the adsorption efficiency and the preferred cyclic hydrocarbonabsorbed.

In one preferred embodiment, the active adsorptive nanocomposite ismechanically mixed with the first aqueous solution at a sufficientmechanical mixing speed of at least 150-500 rpm, preferably at least175-400 rpm, more preferably 190-225 rpm or 200 rpm. In one embodiment,the contacting is carried out for 30 min to 720 min, preferably 45 minto 600 min, more preferably 60 min to 500 min or 480 min

In one embodiment, a dosage of the active adsorptive nanocomposite usedis at least 25%, preferably at least 40%, more preferably at least 50%by mass (mg) of a para-xylene concentration, a toluene concentration orboth (ppm) within the first aqueous solution.

In one embodiment, the first aqueous solution has a pH range from 4-8,preferably 5-7 or a pH of 6.

In one embodiment, the contacting occurs at a temperature range of 20°C. to 30° C., preferably 22 to 27° C.

In one embodiment, the metal oxide nanoparticles are zinc oxide and thecontacting removes at least 70%, preferably at least 73%, preferably atleast 75%, preferably at least 78%, preferably at least 80%, morepreferably 83%, more preferably 85%, more preferably 89% of para-xylenefrom the first aqueous solution.

In one embodiment, the contacting removes at least 87% of para-xylenefrom the first aqueous solution wherein the metal oxide nanoparticlesare preferably zinc oxide, a para-xylene concentration in the firstaqueous solution is at least 100 ppm, the dosage range is 25-150 mgmg/100 ml, the pH is from 5-7, the temperature is from 20-30° C., thecontacting time is 20-720 min and a mixing rate of 150-500 rpm.

In one embodiment, the metal oxide nanoparticles are iron oxide and thecontacting removes at least 60%, preferably at least 65%, preferably atleast 70%, preferably at least 75%, preferably at least 80%, morepreferably 85%, more preferably 86% of para-xylene from the firstaqueous solution.

In one embodiment, the contacting removes at least 86% of para-xylenefrom the first aqueous solution wherein the metal oxide nanoparticlesare iron oxide, a para-xylene concentration in the first aqueoussolution is at least 100 ppm, the dosage is 25-150 mg mg/100 ml, the pHis from 5-7, the temperature is from 20-30° C., the contacting time is20-720 min and a mixing rate of 150-500 rpm.

In one embodiment, the metal oxide nanoparticles are aluminum oxide andthe contacting removes at least 69%, preferably at least 72%, preferablyat least 76%, preferably at least 78%, preferably at least 80%, morepreferably 83%, more preferably 85%, more preferably 89% of para-xylenefrom the first aqueous solution. In one embodiment, the contactingremoves at least 89% of para-xylene from the first aqueous solutionwherein the metal oxide nanoparticles are aluminum oxide, a para-xyleneconcentration in the first aqueous solution is at least 100 ppm, thedosage is 25-150 mg mg/100 ml, the pH is from 5-7, the temperature isfrom 20-30° C., the contacting time is 20-720 min and a mixing rate of150-500 rpm.

In one embodiment, the metal oxide nanoparticles are zinc oxide thecontacting removes at least 11% preferably at least 22%, preferably atleast 48%, preferably at least 51% of toluene from the first aqueoussolution. In one embodiment, the contacting removes at least 51% oftoluene from the first aqueous solution wherein the metal oxidenanoparticles are zinc oxide, a toluene concentration in the firstaqueous solution is at least 100 ppm, the dosage is 25-150 mg mg/100 ml,the pH is from 5-7, the temperature is from 20-30° C., the contactingtime is 20-720 min and a mixing rate of 150-500 rpm. In one embodiment,the metal oxide nanoparticles are iron oxide and the contacting removesat least 17%, preferably at least 32%, preferably at least 52%,preferably at least 54% of toluene from the first aqueous solution.

In one embodiment, the contacting removes at least 54% of toluene fromthe first aqueous solution wherein the metal oxide nanoparticles areiron oxide, a toluene concentration in the first aqueous solution is atleast 100 ppm, the dosage is 25-150 mg mg/100 ml, the pH is from 5-7,the temperature is from 20-30° C., the contacting time is 20-720 min anda mixing rate of 150-500 rpm.

In one embodiment, the metal oxide nanoparticles are aluminum oxide andthe contacting removes at least 17%, preferably at least 22%, preferablyat least 44%, preferably at least 54% of toluene from the first aqueoussolution. In one embodiment, the contacting removes at least 54% oftoluene from the first aqueous solution wherein the metal oxidenanoparticles are aluminum oxide, a toluene concentration in the firstaqueous solution is at least 100 ppm, the dosage is 25-150 mg mg/100 ml,the pH is from 5-7, the temperature is from 20-30° C., the contactingtime is 20-720 min and a mixing rate of 150-500 rpm.

The contacting may be carried out within a variety of vessels dependingon the scale of the application. Examples of vessels include but are notlimited to containers, storage tanks, and reservoirs, Alternateembodiments could be envisioned wherein the contacting occurs byfiltering a portion of the first aqueous solution through a membranecomprising the active adsorptive nanocomposite.

In the present disclosure, the active adsorptive nanocomposite withadsorbed para-xylene, toluene, or both is removed to form a treatedaqueous solution that has a lower para-xylene and/or toluene contentthan the first aqueous solution.

“Removing” as used herein refers to any process of separating chemicaland/or physically distinctive components from one another. The activeadsorptive nanocomposite with adsorbed cyclic hydrocarbons and thetreated aqueous solution exhibit differences inboiling/melting/subliming temperature that may be exploited. Alternativeremoving steps could be envisioned. Examples of alternate removing stepsinclude, filtering, decanting, and evaporating at least a portion of thetreated aqueous solution.

In one embodiment, the first aqueous solution comprises at least 50 ppmpreferably at least 60 ppm, preferably at least 70 ppm, more preferablyat least 80 ppm, more preferably at least 90 ppm, more preferably atleast 100 ppm, more preferably 120 ppm, more preferably 140 ppm, morepreferably at least 170 ppm of para-xylene and/or toluene relative tothe first aqueous solution.

According to a second aspect, the present invention relates to a processfor forming an active adsorptive nanocomposite for use in the method forremoving cyclic hydrocarbons from the first aqueous solution. Theprocess is consistent with production of the active adsorptivenanocomposite described herein, in one or more of their embodiments. Theprocess involves sonicating a sufficient amount of multi-walled carbonnanotubes in a polar solvent to form a dispersion comprisingdeagglomerated carbon nanotubes.

The process described herein is characterized as wet chemistry and isconsidered simple and cost effective compared to other processesfacilitating the binding, embedding or loading of metal oxidenanoparticles to the surface and pore spaces of carbon nanotubes. Theprocess of the present disclosure involves no pre-processing,surface-processing and/or coatings.

In one embodiment, raw carbon nanotubes are dispersed in a polar solventincluding, but not limited to acetone, acetonitrile, methanol, ethanol,n-propanol, methylethylketone, cyclohexanone, diethyl ether, dibutylether, ethyl acetate, isopropyl acetate, butyl acetate, amines,acetamide, methylene chloride, chloroform, hexafluoromethaxylene,dimethylsulfoxide, dimethylformamide or n-methyl-2-pyrrolidone until asubstantially homogeneous dispersion is formed.

In a preferred embodiment, the carbon nanotubes are multi-walled carbonnanotubes, single-walled carbon nanotubes, hybrid nanotubes or mixturesthereof.

In one embodiment, the dispersion does not contain a surfactant. Thenanotubes may be dispersed using sonication to aid the formation of thedispersion. The nanotubes may be dispersed by sonicating for 10-60minutes, preferably 15-45 minutes, more preferably about 30 minutes.Inherent agglomeration prevention properties of the nanoparticlesthemselves may aid dispersion.

In another embodiment, if necessary surfactants can be used to aid inthe dispersion. Surfactants are compounds that lower the surface tension(or interfacial tension) between two liquids or between a liquid and asolid. Surfactants may act as detergents, wetting agents, emulsifiers,foaming agents and dispersants. Surfactants are commonly used to betterdisperse solid nanoparticles in a fluid. They can also make thedispersion easier to process and stabilize the dispersion by inhibitingcrystallization or precipitation of the nanocomposites. Suitablesurfactants include amphoteric, cationic, anionic and nonionicsurfactants. Examples of surfactants include ammonium lauryl sulfate,sodium lauryl sulfate (SDS, sodium dodecyl sulfate), sodium lauryl ethersulfate, sodium myreth sulfate, dioctyl sodium sulfosuccinate,perfluorooctanesulfonate, sodium stearate, octenidine dihydrochloride,cetyl trimethylammonium bromide (CTAB), 5-bromo-5-nitro-1,3-dioxane andthe like.

Subsequently, a metal salt is dissolved in a polar solvent such asacetone, acetonitrile, methanol, ethanol, n-propanol, methylethylketone,cyclohexanone, diethyl ether, dibutyl ether, ethyl acetate, isopropylacetate, butyl acetate, amines, acetamide, methylene chloride,chloroform, hexafluoromethaxylene, dimethylsulfoxide, dimethylformamideand n-methyl-2-pyrrolidone. The metal oxide precursors are generallysalt precursors such as chlorides and nitrates that can precipitate inwater as the oxo-hydroxide form. Precursors of the metal oxide (i.e.metal salt) nanoparticles and carbon nanotubes are added at specificmass ratios. In one embodiment, the mass ratio range of carbon nanotubesto metal salt is from 0.5:1-19:1, 2:1-8:1, 3:1-7:1, 4:1-6:1.

The metal salt is selected with regards to the polar solvent, and servesas a soluble metal oxide nanoparticle precursor for the formation of arespective metal oxide nanoparticle during subsequent processing steps.The mixing results in the impregnation of metal oxide nanoparticleprecursors onto and within the deagglomerated carbon nanotubes. As aresult, metal salts other than metal nitrates could be envisionedincluding but not limited to metal halides, metal carbonates, metalalkoxides and metal hydroxides.

Depending upon the cyclic hydrocarbon targeted for removal a wider arrayof metals could be envisioned. Examples include but are not limited to,copper, magnesium, zirconium, titanium, vanadium, rhodium, rhenium,silicon, molybdenum, thorium, chromium, manganese, cerium, lanthanum,neodymium, praseodymium, samarium, gadolinium, terbium erbium, thulium,ytterbium, lutetium, lead, cadmium, calcium, antimony, tin, bismuth,cobalt, tungsten, and any mixtures thereof.

The reaction conditions may be adjusted depending upon the type of metaloxide precursor being impregnated onto or within the deagglomeratedcarbon nanotubes. In one embodiment, the metal salt solution is addeddropwise to the dispersion of deagglomerated carbon nanotubes. In someembodiments, the mixing may involve sonication. The sonication could beperformed for 10-60 minutes, preferably 15-45 minutes, more preferablyabout 30 minutes. In alternate embodiments heat may be necessary duringthe mixing. Reaction temperature ranges could include 100-225° C.,preferably 120-200° C.

The process also involves removing the polar solvent from thenanocomposite solution to form a dry nanocomposite. Once the mixing iscompleted and the metal oxide nanoparticle precursor has beenimpregnated onto or into the carbon nanotubes, excess dissolved salts,and chemical reagents should be separated. The removing as used hereinrefers to any processing steps that minimize excess dissolved chemicalspecies and/or byproducts that are not critical to the formation of theactive adsorptive nanocomposite.

In one embodiment, the removing comprises cooling the nanocompositesolution to room temperature, filtering the cooled nanocompositesolution to form a nanocomposite filtrate and washing the filtrate atleast once with a suitable solvent selected from deionized water and/orthe polar solvent, for example ethanol. The resulting nanocompositefiltrate is dried at an elevated temperature to remove all solvent andexcess dissolved chemical species and/or byproducts. In one embodimentdrying temperatures could be in the range of 80-120° C., preferably90-110° C., preferably 100° C. The length of drying may be affected bythe choice and amount of solvent. In one embodiment, the removingcomprises filtering to form the nanocomposite filtrate and drying toform the dry nanocomposite.

The process also involves calcining the dry nanocomposite to form theactive adsorptive nanocomposite. The calcining is the conversion stepwhere the impregnated metal oxide nanoparticle precursors mentionedduring the mixing form metal oxide nanoparticles. At elevatedtemperatures metal oxides are a stable chemical product and areenergetically favored. As a result, less stable chemical portions of themetal oxide precursor become gaseous and leave behind the desired metaloxide. The extent to which the metal oxide nanoparticle conversion takesplace and subsequently how effective the resulting adsorptivenanocomposite will be is a function of the calcining temperature andtime of exposure. In one embodiment, calcination is performed at200-400° C. for up to 8 hours, preferably 250-400° C. for up to 6 hours,preferably 300-400° C. for up to 4 hours, preferably 350° C. for 4hours.

The resulting active adsorptive nanocomposite may include carbonnanotubes coated, embedded, or impregnated with nanoparticle metal oxidefor use in the methods of removing cyclic hydrocarbons from aqueoussolution in one or more of their embodiments previously describedherein.

The method of forming the active adsorptive nanocomposite describedherein is a liquid-solid and/or solid-solid transformation. These arethe most broadly used in order to control nanocomposite morphology. Inaddition, gas-solid transformation methods can be envisioned including,but not limited to, chemical vapor deposition (CVD) processes such asmetalorganic, plasma-assisted, thermally activated/pyrolytic and photoCVD methodologies and multiple-pulsed laser deposition.

It is envisioned that the process for producing the active adsorptivenanocomposite for the removal of cyclic hydrocarbons may be adapted toincorporate other techniques. Examples of other techniques that may beused to synthesize the active adsorptive nanocomposite include, but arenot limited to, hot pressing of composite powder, pressure lesssintering technique, direct in-situ growth, in-situ chemical vapordeposition (CVD) synthesis route, pulsed laser deposition,high-intensity ultrasonic radiation method, assembling pre-synthesizedmetal oxide nanoparticles as building blocks on CNTs, spontaneousformation of metal oxide nanoparticles on CNTs, thermal decomposition ofmetal oxide precursors directly onto the surface of carbon nanotubes,hydrothermal crystallization, sol-gel followed by spark plasma sinteringprocess, surfactant wrapping sol-gel method, chemical precipitation andcontrolled hetero-aggregation method.

The examples below are intended to further illustrate protocols forpreparing and characterizing active adsorptive nanocomposites comprisingmetal oxide nanoparticle impregnated carbon nanotubes, and uses thereof.Further they are intended to illustrate assessing these adsorbentmaterials for cyclic hydrocarbon removal efficiency described herein,and are not intended to limit the scope of the claims

Example 1

Chemicals

Commercial multiwall carbon nanotubes were purchased from “Timesnano”with purity of >95% (by weight). Other chemicals which include ironnitrate, aluminum nitrate, zinc nitrate, ethanol, toluene, p-xylene(99.7% purity), nitric acid (>69% purity) and sodium hydroxide ofanalytical grade, were purchased from Sigma Aldrich and used as receivedwithout any further treatment.

Example 2

Preparation of Adsorbent Materials

For impregnation of metal oxide nanoparticles on the surface of CNTs,required amount of CNTs was weighed, poured into sufficient amount ofethanol, and ultra-sonicated for 30 minutes in order to properlydeagglomerate and disperse CNTs in solvent. 10% (weight based on CNTsplus metallic salt) aluminum nitrate salt was dissolved in sufficientamount of ethanol, added to CNTs and was sonicated for further 30minutes. Then, the sample was shifted to oven for drying at 90° C. Aftercomplete drying of ethanol, the sample was calcined in furnace at 350°C. temperature for 4 hours.

Example 3

Adsorption Experiments

Batch adsorption experiments were performed for removal of the cyclichydrocarbon from water. Adsorbents were weighed and added to glassflasks. Distilled deionized water was taken in order to prepare solutionof toluene. Solution of 100 ppm concentration was prepared in avolumetric flask and stirred using magnetic stirrer to get homogeneoussolution. Glass flasks containing adsorbents were filled (100 ml) withtoluene solution and were placed on shaker for specific time (2 hour)and 200 shaking rpm at room temperature. After completion of providedcontact time; samples were removed from shaker and filtered to collectsample for analysis of concentration. The adsorption capacity of thecyclic hydrocarbon on CNTs surface was calculated by following relation

$\begin{matrix}{q = {\frac{\left( {C_{0} - C} \right)}{m}*V}} & (1)\end{matrix}$While;q=Adsorption capacity (mg/g)C₀=Initial concentration of cyclic hydrocarbon in sample (mg/l)C=Final concentration (mg/l)V=Volume of sample (ml)m=Amount of adsorbent (g)Percentage removal was found using following relation.

$\begin{matrix}{{{Removal}\mspace{14mu}(\%)} = {\frac{C_{0} - C}{C_{0}}*100}} & (2)\end{matrix}$

Example 4

Characterization of Adsorbents

Raw CNTs and impregnated CNTs were analyzed using characterizationtechnique of SEM, EDX and TGA analysis. SEM provided the informationabout physical morphology of sample while EDX provided the elementalanalysis of materials. Thermogravimetric analysis was carried out usingTGA equipment in order to check the thermal degradation and purity ofmaterials.

Example 5

Concentration of Adsorbate

Concentration of toluene, para-xylene or both in water was determinedusing COD analysis. Ready-made COD analysis vials were filled with 2 mlof sample and digested for 120 minutes at 150° C. temperature. Afterdigestion samples were cooled at room temperature and then analyzedusing photo spectrometer (Hach Model: DR3900).

Example 6

Characterization of Adsorbents

FIGS. 1A, 1B, 1C, and 1D represent the SEM image of both raw and metaloxide nanoparticles impregnated MWCNTs. All images were taken using 15KV energy and view filed of 3 μm while at resolution of 63×. It isobserved that surface of raw CNTs was smooth but more agglomerated inshown in part. Metal oxides nanoparticles impregnated CNTs appear moredispersed and presences of metal oxide nanoparticles impregnation onCNTs can be observed in yellow circles.

FIGS. 7A, 7B, 7C, and 7D provide EDX analysis and presence of carbonpeak as main constituent in all samples and impregnated metal oxides inrespective samples can be verified. Nickel peak appear in all samplesbecause nickel was used for growing CNTs. FIG. 3 indicates the TGA ofboth raw and metal oxide nanoparticles impregnated CNTs. It can beobserved that after a small weight loss initially due to moisturepresence, all materials were stable up to 450° C. Raw CNTs startedburning around 530° C. while iron oxide and zinc oxide impregnated CNTsdegraded around 450° C. due to higher thermal conductivity of zinc oxideand iron oxide. There was no change in burning temperature of samplecontaining aluminum oxide nanoparticles because alumina has low thermalconductivity. It can also be observed that that the residual weightpercentage of ash at the end of analysis was around 1.5% for raw CNTsand it was around 7% for all metal oxide nanoparticles impregnated CNTs.Higher weight residue for impregnated CNTs is representation of metaloxide nanoparticles left at the end of experiment.

The invention claimed is:
 1. A method for removing a cyclic hydrocarbonfrom a first aqueous solution comprising para-xylene, toluene, or both,the method comprising: mixing zinc nitrate and carbon nanotubes to formzinc-doped carbon nanotubes; calcining the zinc-doped carbon nanotubesto form an active adsorptive nanocomposite; contacting the activeadsorptive nanocomposite with the first aqueous solution to adsorb atleast a portion of the para-xylene, toluene, or both onto at least onesurface of the active adsorptive nanocomposite; and removing the activeadsorptive nanocomposite with adsorbed para-xylene, toluene, or bothfrom the first aqueous solution to form a treated aqueous solution thathas a lower para-xylene and/or toluene content than the first aqueoussolution; wherein the active adsorptive nanocomposite comprises carbonnanotubes, and zinc oxide nanoparticles attached to a surface of thecarbon nanotubes, wherein the zinc oxide nanoparticles are present in1-15% by weight, relative to the total weight of the active adsorptivenanocomposite.
 2. The method of claim 1, wherein the contactingcomprises mechanically mixing and/or sonicating the active adsorptivenanocomposite with the first aqueous solution.
 3. The method of claim 2,wherein the active adsorptive nanocomposite is mechanically mixed withthe first aqueous solution with a mechanical mixing speed of at least200 rpm.
 4. The method of claim 1, wherein the active adsorptivenanocomposite is contacted with the first aqueous solution at a weightper volume ratio of at least 25-150 mg of the active adsorptivenanocomposite per 100 mL of the first aqueous solution.
 5. The method ofclaim 1, wherein the contacting is carried out for 30 min to 720 min. 6.The method of claim 1, wherein the active adsorptive nanocomposite iscontacted with the first aqueous solution a temperature range of 20° C.to 30° C.
 7. The method of claim 1, wherein the first aqueous solutioncomprises at least 100 ppm of para-xylene and/or toluene.
 8. The methodof claim 1, wherein the metal oxide nanoparticles are zinc oxide and thecontacting removes at least 77% of the para-xylene from the firstaqueous solution.
 9. The method of claim 1, wherein the first aqueoussolution has a pH range from 5-7 during the contacting.